Printable composition with nanostructures of first and second types

ABSTRACT

A printable composition for use in forming a printed element by printing and curing is described. The printable composition comprises a plurality of nanostructures of a first type that, upon printing and curing, form an arrangement defining intermediate volumes thereamong. The printable composition further comprises a plurality of nanostructures of a second type that, upon printing and curing, at least partially fill the intermediate volumes to promote smooth surface topography and reduced porosity in the printed element.

FIELD

This patent specification relates to printable compositions havingnanostructural ingredients and the printing of functional materialstherewith.

BACKGROUND

The field of printed electronics, and more generally the field ofprinted functional materials, represents a promising avenue toward a newworld of devices ranging from flexible, low-cost computer displays tolightweight, high-capacity storage batteries. Using printingtechnologies traditionally associated with the creation ofhuman-readable text or graphics, special printable compositions or“inks” are transferred to surfaces and cured into functional elementssuch as conductors, semiconductors, and dielectrics. Multilayerstructures can be built in an additive process, i.e., by printingadditional layers of elements on top of previously-cured elements, tocreate more complex structures such as thin-film transistors.

Although several advantages can be brought about in terms of deviceflexibility, cost, durability, and the like, the electrical performanceoffered by today's printed semiconductors is generally inferior to theperformance of single-crystal semiconductors used in most of today'shigh-speed electronics and computing equipment. Whereas single-crystalsilicon semiconductors may offer mobilities in the range of 800-1000cm²/V-s, which can facilitate device switching speeds in the MHz and GHzrange, printed semiconductor elements such as pentacene, a p-typeorganic semiconductor, may only offer mobilities on the order of 2-3cm²/V-s.

One issue can arise in the fabrication of functional printed elementswhen the printable composition contains nanostructures intended toimpart certain characteristics to the cured printed element, such ascertain electrical characteristics (e.g., conductive, semiconductive,dielectric, etc.). Upon thermal treatment or other curing method, anddue at least in part to a volume shrinkage of a molecular precursoraccompanying the nanostructures in the printable composition, themorphology of the resulting printed element can be porous, and thesurface of the resulting printed element can be rough. This, in turn,can bring about difficulty in properly printing a subsequent layer ontop of the printed element. It would be desirable to provide for reducedporosity and smoother surface topography in the printed element.

SUMMARY

In accordance with an embodiment, a printable composition for use informing a printed element is provided. The printable compositioncomprises a plurality of nanostructures of a first type that, uponprinting and curing, form an arrangement defining intermediate volumesthereamong. The printable composition further comprises a plurality ofnanostructures of a second type that, upon printing and curing, at leastpartially fill the intermediate volumes to promote smooth surfacetopography and reduced porosity in the printed element.

Also provided is a method for fabricating a printed element, in which acomposition is transferred onto a surface according to a printingprocess and cured to form the printed element. The composition comprisesa plurality of nanostructures of a first type and a plurality ofnanostructures of a second type, the nanostructures of the second typeat least partially filling space between the nanostructures of the firsttype in the printed element.

Also provided is a printed circuit element comprising a plurality ofnanostructures of a first type in an arrangement defining intermediatevolumes thereamong, and a plurality of nanostructures of a second typeat least partially filling the intermediate volumes. The printed circuitelement is formed by a transfer of an ink solution comprising thenanostructures of the first and second types to a surface according to aprinting process and by a curing of the transferred ink solution.

Also provided is an ink formulation for a printer, comprising a firstpercentage by weight of elongate nanostructures having an aspect ratioabove about 3:1, and a second percentage by weight of compactnanostructures having an aspect ratio below about 2:1. The secondpercentage is between about 0.2 and 100 times the first percentage.

Also provided is an apparatus comprising means for transferring aprintable composition to a surface, the printable composition comprisinga plurality of nanostructures of a first type that, upon transfer to asurface and curing, form an arrangement defining intermediate volumesthereamong. The printable composition further comprises a plurality ofnanostructures of a second type that, upon transfer to the surface andcuring, at least partially fill the intermediate volumes to promotesmooth surface topography and reduced porosity in the resultant printedelement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a printable composition according to an embodiment;

FIG. 2 illustrates examples of elongate nanostructures according to oneor more embodiments;

FIG. 3 illustrates examples of compact nanostructures according to oneor more embodiments;

FIG. 4 illustrates fabricating a printed element according to anembodiment;

FIG. 5 illustrates a surface upon which a printable composition is beingtransferred by an inkjet printer according to an embodiment;

FIG. 6 illustrates transferred and cured printable composition havingelongate nanostructures but not having compact nanostructures;

FIG. 7 illustrates transferred and cured printable composition accordingto an embodiment; and

FIG. 8 illustrates transferred and cured printable composition accordingto an embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a printable composition 102 according to anembodiment, comprising a carrier solution 104, a plurality ofnanostructures of a first type, and a plurality of nanostructures of asecond type. By way of non-limiting example, the nanostructures of thefirst type can be similar to elongate nanostructures 106, while thenanostructures of the second type can be similar to compactnanostructures 108. However, other types of nanostructures can be usedin other embodiments. Printable composition 102 further comprises amolecular precursor substantially dissolved in the carrier solution 104,the molecular precursor being selected such that it decomposes into adesired solid material upon transfer and curing. In one embodiment, themolecular precursor is selected such that the decomposed precursor solidcomprises amorphous or polycrystalline versions of the material used forthe elongate nanostructures 106. In another embodiment, the molecularprecursor is selected such that, upon transfer to a surface inconjunction with the carrier solution 104, a saturation condition occursthat facilitates in situ growth of crystalline or polycrystallineversions of the elongate nanostructural material.

FIG. 2 illustrates examples 202-212 of elongate nanostructures 106 thatmay be used in the printable composition 102 of FIG. 1. The elongatenanostructures 106 may comprise nanowires, nanorods, nanodiscs,nanoplates, or any of a variety of other anisometric nanostructureshaving major dimensions D1 that are substantially greater than theirminor dimensions D2, as illustrated in FIG. 2. Depending on theparticular application, the elongate nanostructures 106 can compriseconductive, a semiconductive, or dielectric material. Other examples caninclude phosphorus. In one embodiment, the elongate nanostructures 106have an aspect ratio (the ratio of their major dimension D1 to theirminor dimension D2) that is greater than 3:1. In another embodiment, theelongate nanostructures 106 have an aspect ratio that is greater than5:1.

It is to be appreciated that FIG. 2 illustrates only a few examples ofthe many types of elongate nanostructures that may be used in accordancewith the present teachings. Moreover, different shapes of elongatenanostructures can be mixed together without departing from the scope ofthe present teachings. For example, half of the elongate nanostructures106 may comprise nanowires similar to element 202 of FIG. 2, while theother half may comprise nanodiscs similar to element 208 of FIG. 2.Although the particular elements 202-212 illustrated in FIG. 2 are solidthroughout, in other embodiments the elongate nanostructures 106 cancomprise hollow nanocylinders or other shapes that are not solidthroughout.

FIG. 3 illustrates examples 302-308 of compact nanostructures 108 thatmay be used in the printable composition 102 of FIG. 1. The compactnanostructures 108 may comprise any of a variety of compact shapes inwhich a major dimension D1 is generally comparable to a minor dimensionD2. For example, the compact nanostructures 108 may be generallyglobular, as illustrated by the spheroid shape 302 or the ellipsoidshape 306 in FIG. 3. Alternatively, the compact nanostructures 108 maycomprise truncated nanowires 308 as illustrated in FIG. 3, or othershapes such as the pyramidal shape 304. In one embodiment, the compactnanostructures 108 have an aspect ratio that is less than 3:1. Inanother embodiment, the compact nanostructures 108 have an aspect ratiothat is less than 2:1.

The compact nanostructures 108 can comprise conductive, semiconductive,or dielectric material. Other examples can include phosphorus. In oneembodiment, the compact nanostructures 108 comprise a material identicalto the material used for elongate nanostructures 106, while in otherembodiments, the materials can be different. As with the elongatenanostructures 106, the compact nanostructures 108 can be mixed andmatched from among different shapes, e.g., half of the compactnanostructures can be similar to the spheroid shape 302 of FIG. 3, whilethe other half can be similar to the truncated nanowire shape 308 ofFIG. 3. As with the elongate nanostructures 106, the compactnanostructures 108 can comprise shapes that are solid throughout, orthat are not solid throughout.

FIG. 4 illustrates fabricating a printed element according to anembodiment. At step 402, the printable composition 102 is preparedincluding elongate nanostructures 106 and compact nanostructures 108. Atstep 404, the printable composition 102 is transferred to a surfaceaccording to a printing process.

FIG. 5 illustrates a surface 504 to which a printable composition isbeing transferred according to an inkjet printing process. An inkjetprinthead 502 containing the ink, i.e., the printable composition 102,is swept across the surface 504 in a manner analogous to the way blackor colored ink is deposited on paper by a commercially available inkjetprinter, such that printed elements 506 are formed. The example of FIG.5 simply shows the printed elements 506 as being parallel straightlines, it being appreciated that specific layouts are programmed intothe printer drivers for the inkjet printing apparatus to form variouscircuit elements such as electrical conductors, resistors, capacitorplates, capacitor dielectrics, transistor sources/gates/drains, etc. Anyof a wide variety of printing processes can be used at step 404including, but not limited to, inkjet printing, drop-on-demand printing,screen printing, micro-contact printing, gravure printing, flexographyprinting, letterpress printing, and electrostatic printing.

At step 406, the printed elements 506 are cured, such as by a sinteringprocess. In one embodiment, the sintering temperature is low enough suchthat the elongate and compact nanostructures are not melted, but highenough such that the liquid content in the printable composition willevaporate and the molecular precursor will decompose into the desiredsolid material. At step 408, upon curing, the compact nanostructures 108fill spaces between the elongate nanostructures 106 to promote lessporous morphology and smoother surface topography in the printedelements 506. Subsequent layers of printed elements can then be appliedas needed to form the desired functional device.

FIG. 6 illustrates, for purposes of clarity and comparison, ahypothetical cross-section of a printed element near a surface thereoffor a circumstance in which elongate nanostructures 602 are present inthe printable composition but compact nanostructures are not present.The elongate nanostructures 602 form a haystack-like arrangement, withdecomposed molecular precursor 604 also being present and acting as akind of physical and electrical “glue” for proximal elongatenanostructures 602. Intermediate regions lying among the elongatenanostructures 602, as represented by the intermediate region 610 lyingamong the elongate nanostructures 602 a, 602 b, and 602 c, can besubstantially unoccupied, being only partially filled with material suchas the decomposed molecular precursor 604. As illustrated, themorphology of the printed element can be porous, and the surface can berough. Notably, depending on the particular substances and environmentsof the printing process, the elongate nanostructures could alternativelybecome arranged in a parallel fashion. However, even in this case theprinted element can have substantial porosity and/or surface roughness.

FIG. 7 illustrates, for purposes of clarity and comparison, ahypothetical cross-section of a printed element near a surface thereoffor a circumstance in which both compact nanostructures 704 and elongatenanostructures 702 are present in the printable composition according toan embodiment. The elongate nanostructures 702 form a generally randomarrangement that defines intermediate volumes thereamong, as representedby the intermediate volume 710 positioned among the elongatenanostructures 702 a, 702 b, and 702 c. As illustrated, the presence ofthe compact nanostructures 704 in the intermediate volumes 710 promotesreduced porosity and a smoother surface in the resultant printedelement. Moreover, the electrical properties of the printed element canbe substantially enhanced, because electrical connectedness of theelongate nanostructures 702 is also promoted. The present teachings arealso applicable where the elongate nanostructures become arranged in aparallel fashion, the compact nanostructures promoting smoother surfacesand reduced porosity in that arrangement as well.

In one particularly advantageous embodiment, the elongate nanostructures702 and the compact nanostructures 704 each comprise an identicalsemiconducting material, and the resultant printed element is asemiconducting element having a carrier mobility substantially improvedby the presence of the compact nanostructures in the intermediatevolumes 710. In another particularly advantageous embodiment, theelongate nanostructures 702 and the compact nanostructures 704 eachcomprise an identical conductor, and the resultant printed element is aconductor with a conductance that is substantially improved by thepresence of the compact nanostructures in the intermediate volumes 710.

Various details relating to the above description, FIGS. 1-7, and thepresent teachings are presented hereinbelow, but should not be construedas limiting the scope of the present teachings. In one embodiment, theelongate nanostructures are nanorods having a length of roughly 200 nmand a diameter of roughly 10 nm. In other embodiments, the elongatenanostructures may be substantially thinner or thicker, having a minordimension (i.e., diameter) between 2 nm and 100 nm, for example. Upontransfer and cure without the compact nanostructures of the presentteachings, the nanorods would form a generally random arrangementsimilar to that of FIG. 6. Some degree of electrical connectivity amongthe nanorods could be achieved solely by virtue of this haystack-likearrangement, and the overall printed element could achieve some degreeof electrical utility. However, in accordance with an embodiment,compact nanostructures having a generally globular shape are included inthe printable composition. The resulting printed element, also referredto as a thin film, enjoys reduced porosity, smoother topography, and ahigh degree of physical and electrical connectedness to yield improvedoverall physical and electrical performance. In one example, which ispresented by way of example and not by way of limitation, the compactnanostructures are roughly spherical (D1=D2) and have a diameter of 7 nmwhere the elongate nanostructures are nanorods having a length ofroughly 200 nm and a diameter of roughly 10 nm.

In one embodiment, a major dimension of the compact nanostructures isless than a minor dimension of the elongate nanostructures, as with thepreceding example. In other embodiments, a major dimension of thecompact nanostructures can be comparable to a minor dimension of theelongate nanostructures. In still other embodiments, a major dimensionof the compact nanostructures can be substantially greater than a minordimension of the elongate nanostructures, provided that the compactnanostructures are small enough to populate the intermediate volumesamong the elongate nanostructures in the cured printed element in amanner that facilitates smooth surface topography and reduced porosity.

Elongate and compact nanostructures that may be used in accordance withthe present teachings may be fabricated in any of a variety of ways. Forexample, single crystal nanowires may be grown using methods such asvapor-liquid-solid (VLS) catalytic growth, solution-liquid-solid (SLS)catalytic growth, and non-catalytic vapor-phase epitaxy. Other methodsfor producing nanowires include template-assisted synthesis, nanoimprintlithography, dip-pen nanolithography, self-assembly of nanoparticles,solution phase methods based on capping reagents, and solvothermalmethods.

In one embodiment in which the elongate nanostructures are nanorods 200nm in length and 10 nm in diameter, and in which the compactnanostructures are approximately 7 nm globes, the printable compositioncomprises 2.0% by weight of the nanorods and 3.0% by weight of thecompact nanostructures. The ratio by weight of compact nanostructures toelongate nanostructures in the printable composition can generally rangebetween about 0.2 to 100 without departing from the scope of the presentteachings. The appropriate ratio by weight of compact nanostructures toelongate nanostructures for a particular circumstance will be highlydependent on the particular sizes and contours of the elongatenanostructures, which affects how tightly or loosely they will arrange,and also on the particular sizes and shapes of the compactnanostructures, which will affect how efficiently they can fill theintermediate volumes among the elongate nanostructures. Where theelongate nanostructures are straight nanowires and the compactnanostructures are globular, a ratio by weight of compact nanostructuresto elongate nanostructures between about 0.5 to 2 often provides forgood morphology and smooth surface topography.

A wide range of viscosities for the printable composition are within thescope of the present teachings. In some embodiments, the printablecomposition comprises a highly non-viscous solution in which the solidcontent (primarily the elongate and compact nanostructures) isrelatively low, e.g. 3 percent or less. In other embodiments, theprintable composition can comprise a highly viscous solution, evenapproaching 90 percent. In some embodiments, the printable compositioncan have a relatively low viscosity on the order of 10-20 centipoise,while in other embodiments the printable composition can have arelatively high viscosity on the order of 200 centipoise or greater.

Among other advantages according to the present teachings, desirableelectrical characteristics such as high conductivity and high mobilitycan be achieved without requiring a melting or liquid-phase fusing ofthe nanostructural material during the curing/sintering process. Thisprovides an ability to cure/sinter at relatively low temperatures,including “plastic-friendly” temperatures, thereby widening the choiceof available substrates (surfaces) and the variety of devices that canbe fabricated.

In the particular context of semiconducting devices, while certain knownorganic printed semiconductors might be cured at relatively lowtemperatures, such organic semiconductors generally suffer fromrelatively low carrier mobilities, as in the pentacene example supra.When implemented in the context of inorganic semiconductor materials,the present teachings can provide for the higher-mobilities associatedwith inorganic semiconductors, while at the same time providing forrelatively low curing/sintering temperatures including“plastic-friendly” temperatures. In one embodiment, the sinteringtemperature using a printable composition containing inorganicsemiconductors according to the present teachings can be about 500degrees Celsius or less, while the resultant printed element can havecarrier mobilities greater than about 10 cm²/V-s. In some embodiments,the resultant printed element can have carrier mobilities greater thanabout 1 cm²/V-s. Yet another advantage according to the presentteachings is reduced shrinkage of the printed element during thesintering process, which can thereby reduce lateral and verticalstresses on device components during and after the curing process.

Where a conducting printed element is desired, examples of conductingmaterials for the elongate and compact nanostructures include gold,silver, platinum, or other highly conductive metals. Where a dielectricprinted element is desired, examples of (non-air) dielectric materialsfor the elongate and compact nanostructures include Ta₂O₅, SiO₂, andAl₂O₃. Where a semiconducting printed element is desired, examples ofsemiconducting materials for the elongate and compact nanostructuresinclude ZnO, CdS, CdSe, ZnS, PbS, GaAs, InP, InO, InSnO, and InZnO. Thesemiconducting materials can be pre-doped for negative or positivecarriers, i.e., the p-doping or n-doping can be performed in conjunctionwith the fabrication of the elongate and/or compact nanostructures priorto formation of the printable composition.

For a nanostructure material of ZnO in which the elongate nanostructuresare 2.0 percent by weight of the printable composition and the compactnanostructures are 3.0 percent by weight of the printable composition,one suitable molecular precursor comprises zinc 2-ethylhexanoate (1.0percent of the printable composition by weight) and 2-ethylhexanoic acid(0.2 percent of the printable composition by weight). In thisembodiment, the carrier solution can comprise isopropanol (93.8 percentof the printable composition by weight).

More generally, the carrier solution can comprise solvent, surfactantsand/or other additives that will further aid in film formation and goodfilm morphology. By way of example and not by way of limitation, thecarrier solution can comprise solvents such as water or isopropanol withor without a surfactant or other additives to assist with suspensionand/or distribution of the suspended nanostructures. The surfactant canserve as a wetting agent and/or an encapsulation agent for thenanostructures in the carrier solution. In some embodiments, ionicsurfactants are used that have either water soluble or hydrophilicfunctional groups. Examples of anionic surfactants that can be usedinclude, but are not limited to, sodium dodecylsulfate (SDS), sodiumdeoxycholate (DOC), and N-lauroylsarcosine sodium salt. Examples ofcationic surfactants that can be used include, but are not limited to,lauryldimethylamine oxide (LDAO), cetyltrimethylammonium bromide (CTAB),and bis(2-ethlyhexyl)sulfosuccinate sodium salt. Any of the above sodiumsalts may alternatively be a lithium salt or a potassium salt.

In some embodiments, the carrier solution can comprise pH modifiers.Examples of pH modifiers for the above-described example include bases,such as sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia(NH₃), and methaneamine (CH₃NH₂), and acids, such as hydrochloric acid(HCl), sulfuric acid (H₂SO₄), and acetic acid (CH₃COOH). Certain buffersalso may be employed as pH modifiers.

For a nanostructure material of ZnO, the molecular precursor cancomprise one or more of ZnO, Zn(NO₃)₂, ZnSO₄, ZnCl₂, and Zn(C₂H₃O₂)₂within an aqueous carrier solution. For a nanostructure material of CdS,the molecular precursor can comprise one or more of cadmium citrate,cadmium chloride, and thioreau. For a nanostructure material of CdSe,the molecular precursor can comprise one or more of cadmium citrate andN,N-dimithyl-selenourea. For a nanostructure material of ZnS, themolecular precursor can comprise one or more of ZnSO₄ and SC(NH₂)₂. Fora nanostructure material of PbS, the molecular precursor can compriseone or more of Pb(NO₃) and SC(NH₂)₂.

FIG. 8 illustrates a hypothetical cross-section of a printed elementnear a surface thereof where a printable composition is transferred andcured according to an embodiment, the printable composition comprising aplurality of nanostructures of a first type in an arrangement definingintermediate volumes thereamong, the printable composition furthercomprising a plurality of nanostructures of a second type at leastpartially filling the intermediate volumes. By way of example, thenanostructures of the first type can be similar to the largernanostructures 802 of FIG. 8, while the nanostructures of the secondtype can be similar to the smaller nanostructures 804. It is to beappreciated that while the larger nanostructures 802 and smallernanostructures 804 of FIG. 8 are shown to be spherical, in otherembodiments they can be pyramidal, cubical, or otherwise comprisingmulti-sided volumes. It still other embodiments, they can be ellipticalor otherwise oddly-shaped. The larger nanostructures 802 form anarrangement that defines intermediate volumes thereamong, as representedby the intermediate volume 810 positioned among the largernanostructures 802 a, 802 b, 802 c, and 802 d. Decomposed molecularprecursor 806 further fills part of the intermediate volumes 810. Asillustrated, the presence of the smaller nanostructures 804 in theintermediate volumes 810 promotes reduced porosity and a smoothersurface in the resultant printed element. Moreover, the electricalproperties of the printed element can be substantially enhanced, becauseelectrical connectedness of the larger nanostructures 802 is alsopromoted. While the larger nanostructures 802 are shown in FIG. 8 asforming a generally random arrangement, in other embodiments they canbecome arranged in a more regular fashion, the smaller nanostructures804 promoting smoother surfaces and reduced porosity in that arrangementas well.

Whereas many alterations and modifications of the embodiments will nodoubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that theparticular embodiments shown and described by way of illustration are inno way intended to be considered limiting. By way of example, althoughsome embodiments supra are described as having all of the elongatenanostructures made from the same material (i.e., all conducting, allsemiconducting, all dielectric), it is not outside the scope of thepresent teachings to mix conducting and semiconducting elongatenanostructures, or to mix conducting and dielectric elongatenanostructures, and so on, depending on the particular resultantelectrical properties desired. Likewise, the compact nanostructures cancomprise mixtures of conducting, semiconducting, and dielectricmaterials without departing from the scope of the present teachings.

By way of further example, although some embodiments supra are describedin terms of the elongate nanostructures being randomly oriented in thecured printed element, in other embodiments the elongate nanostructurescan be uniformly or quasi-uniformly oriented without departing from thescope of the present teachings. By way of still further example, whilecertain embodiments supra are particularly advantageous when thenanostructures are inorganic semiconductors and the molecular precursoris configured to decompose into amorphous or polycrystalline versions ofthat inorganic material, one or more of the elongate nanostructures,compact nanostructures, molecular precursors, carrier solution, anddecomposed molecular precursors can comprise organic semiconductorcompounds or other organic compounds without departing from the scope ofthe present teachings.

By way of still further example, while the molecular precursor supra isdescribed as decomposing into amorphous or polycrystalline structures,often of the same material as the nanostructures, the molecularprecursor could alternatively form epitaxially grown single-crystalextensions of the nanostructure crystals, or otherwise form epitaxiallygrown single-crystal versions of the nanostructural material or othermaterial, without departing from the scope of the present teachings. Byway of even further example, although one or more embodiments supra isparticularly advantageous where the elongate nanostructures form agenerally random arrangement upon printing and curing, in otherpreferred embodiments the elongate nanostructures form a generallyordered arrangement, e.g., generally parallel to each other, with thecompact nanostructures occupying space between the elongatenanostructures for reducing porosity and/or surface smoothness in thecured printed element. Thus, reference to the details of the describedembodiments are not intended to limit their scope.

1-21. (canceled)
 22. A printed circuit element, comprising: a pluralityof nanostructures of a first type in an arrangement definingintermediate volumes thereamong; and a plurality of nanostructures of asecond type at least partially filling said intermediate volumes, saidprinted circuit element being formed by a transfer of an ink solutioncomprising said nanostructures of the first and second types to asurface according to a printing process and by a curing of thetransferred ink solution.
 23. The printed circuit element of claim 22,wherein said nanostructures of the first type are elongatenanostructures, and wherein said nanostructures of the second type arecompact nanostructures.
 24. The printed circuit element of claim 23,said elongate nanostructures generally having aspect ratios greater thanabout 3:1, said compact nanostructures generally having aspect ratiosless than about 2:1, and wherein a ratio by weight of said compactnanostructures to said elongate nanostructures in said printed circuitelement is between about 0.2 and
 20. 25. The printed circuit element ofclaim 24, wherein said compact nanostructures are generally globularwith a major dimension less than a minor dimension of said elongatenanostructures.
 26. The printed circuit element of claim 25, whereinsaid minor dimension of said elongate nanostructures is between about 2nm and 100 nm.
 27. The printed circuit element of claim 23, wherein saidelongate nanostructures comprise an inorganic semiconductor material,and wherein the printed circuit element is operable as a semiconductorcircuit element having a carrier mobility greater than about 1 cm²/V-s.28-33. (canceled)
 34. An apparatus comprising means for transferring aprintable composition to a surface, said printable compositioncomprising a plurality of nanostructures of a first type that, upontransfer to a surface and curing, form an arrangement definingintermediate volumes thereamong, said printable composition furthercomprising a plurality of nanostructures of a second type that, uponsaid transfer and curing, at least partially fill said intermediatevolumes to promote smooth surface topography and reduced porosity in aresultant printed element.
 35. The apparatus of claim 34, wherein saidnanostructures of the first type are elongate nanostructures, andwherein said nanostructures of the second type are compactnanostructures.
 36. The apparatus of claim 35, wherein said elongatenanostructures generally have aspect ratios greater than about 3:1,wherein said compact nanostructures generally have aspect ratios lessthan about 2:1, and wherein a ratio by weight of said compactnanostructures to said elongate nanostructures in said printablecomposition is between about 0.2 and
 100. 37. The apparatus of claim 36,said printable composition further comprising a molecular precursorthat, upon said transfer and curing, forms decomposed precursor solidsfurther filling said intermediate volumes.
 38. The apparatus of claim37, said elongate nanostructures comprising a crystalline version of acompound, said decomposed precursor solids comprising an amorphousversion of said compound, a polycrystalline version of said compound, oran epitaxially grown single-crystal version of said compound.